From what I read in the other posts, even if you play with less than 6 players, there are means to evolve the entire map, as if you were playing with a party of 6.
Is it possible, instead, to play with 2 and develop only 2 areas of the map, and then do it again for 2 more times, on the same map?
No. The other charters are developed automatically, because they have to be. You will eventually need to pull resources from multiple charters, not just yours.